1. Field of the Invention
This invention relates to a surface mounting type electronic circuit unit on which a semiconductor bare chip and a capacitor are mounted, and particularly relates to an electronic circuit unit that is suitably used as a high frequency device.
2. Description of the Related Art
Generally, an electronic circuit unit used as a high frequency device is fabricated by soldering various circuit parts such as chip resistors and chip capacitors on soldering land of conducting patterns formed on a substrate. However, a small-sized electronic circuit unit fabricated by forming thin film circuit elements on a substrate by means of thin film forming technique has been developed with recent progress of integrated circuit fabrication technology.
In the case where a circuit structure required for an electronic circuit unit includes, for example, a transistor and a plurality of capacitors, a method is employed in which a plurality of thin film capacitors and a wiring pattern are formed on a substrate by means of thin film forming technique and a transistor bare chip is mounted and wire-bonded on a substrate. Herein, the thin film capacitor is formed by laminating a bottom electrode, a dielectric layer, and a top electrode successively, and a part of a wiring pattern is served as the bottom electrode and top electrode. Furthermore, the bottom side collector electrode of a transistor is connected to a connection land with conductive adhesive, the top side emitter electrode and base electrode are connected to a bonding pad with a wire, and the wiring pattern is served also as the connection land and bonding pad.
Recently, the technique for miniaturizing the circuit parts such as chip parts and transistor has been progressed markedly, and for example, the ultra-small chip resistor and chip capacitor having an apparent size of approximately 0.6xc3x970.3 mm have been used practically. Therefore, it is possible that such small-size chip parts and transistor are used for the above-mentioned convention electronic circuit unit and are mounted on a substrate with narrow pitch between circuit parts to thereby miniaturize the electronic circuit unit to a certain extent. However, the miniaturization of the circuit parts such as chip parts and transistor is limited, and narrowing of the pitch between parts is limited because many circuit parts should be mounted on a substrate so that soldered portions of individual circuit parts are prevented from short-circuiting. These limitations have prevented further miniaturization of the electronic circuit unit.
Furthermore, according to the above-mentioned conventional electronic circuit unit, the electronic circuit unit can be miniaturized to some extent because at least a plurality of capacitors are formed on a substrate by means of thin film forming technique, however, because a plurality of capacitors and wiring patterns are formed in the limited area on a substrate by means of thin film forming technique, it is difficult to miniaturize the electronic circuit unit further.
Furthermore, in the case where an electronic circuit unit of this type has an amplifier circuit and the emitter of a transistor used as an amplifier circuit is grounded through a capacitor, a method in which the bottom electrode or top electrode of a thin film capacitor is connected to a bonding pad through a wiring pattern and the emitter electrode is connected to the bonding pad by means of wire bonding has been employed in the above-mentioned conventional art. This method is disadvantageous because the high frequency characteristic can be poor due to the inductance of the wiring pattern interposed between the thin film capacitor and bonding pad.
The present invention has been accomplished in view of the problem of the conventional art, and it is the object of the present invention to provide an electronic circuit unit that is suitable for miniaturization and excellent in high frequency characteristic.
As the first means of the present invention to achieve the above-mentioned object, an electronic circuit unit of the present invention comprises a conducting pattern formed on an alumina substrate by means of thin film forming technique, circuit elements including capacitors, resistors, and inductance elements formed on the alumina substrate by means of thin film forming technique so as to be connected to the conducting pattern, and a semiconductor bare chip fixed to the conductive pattern by means of wire bonding, wherein the area of the connection land on which the semiconductor bare chip is mounted is smaller than the bottom surface area of the semiconductor bare chip.
According to the above-mentioned structure, because circuit elements including capacitors, resistors, and inductance elements are formed with high precision by means of thin film forming technique and a semiconductor bare chip is fixed by means of wire bonding, necessary circuit parts are mounted in high density on an alumina substrate and a surface mounting type electronic circuit unit that is suitable for miniaturization is realized. Furthermore, because the area of the connection land on which the semiconductor bare chip is mounted is smaller than the bottom surface area of the semiconductor bare chip, conductive adhesive applied on the connection land such as cream solder or conducting paste can be retained inside the contour of the semiconductor bare chip, and it is prevented that the conductive adhesive spews from the contour of the semiconductor bare chip to result in short-circuit to the surrounding conducting pattern.
In the above-mentioned structure, it is desirable that at least two sides of the rectangular bare chip are located apart from the contour of the connection land. Thereby, the conductive adhesive can be retained inside the contour of two sides of the semiconductor bare chip, spewing of the conductive adhesive is prevented more effectively.
Furthermore, in the above-mentioned structure, it is desirable that an opening is formed in the connection land. Thereby, the excessive conductive adhesive can be retained in the opening, and spewing of the conductive adhesive is more surely prevented.
Furthermore, as the second means to achieve the above-mentioned object, an electronic circuit unit of the present invention has the structure in which a capacitor is formed by laminating a bottom electrode and top electrode with interposition of a dielectric material on a substrate, and a semiconductor bare chip is mounted so as to be located on the capacitor on the substrate, wherein the top electrode of the capacitor is served as a part of a connection land connected to the bottom side electrode of the semiconductor bare chip.
According to the structure as described hereinabove, because the thin film capacitor is formed just under the space where the semiconductor bare chip is mounted, the areal efficiency of the substrate is improved because the semiconductor bare chip and thin capacitor are placed one on the other, and the electronic circuit unit made even more small-sized. Furthermore, because the top electrode of the thin film capacitor is served also as a part of the connection land that is connected to the bottom side electrode of the semiconductor bare chip, the lead inductance component between the thin film capacitor and the semiconductor bare chip is reduced, and the deterioration of high frequency characteristic is prevented.
As another means to achieve the above-mentioned object, the electronic circuit unit of the present invention has the structure in which a capacitor is formed by laminating a bottom electrode and a top electrode with interposition of a dielectric material on a substrate, and a semiconductor bare chip is mounted on the substrate, wherein the top electrode of the capacitor is connected to the top side electrode of the semiconductor bare chip by means of wire bonding.
According to the above-mentioned structure, because the top side electrode of the semiconductor bare chip is wire-bonded by use of the top electrode of the thin film capacitor as a bonding pad, the areal efficiency of the substrate is improved by the area corresponding to the bonding pad, and the electronic circuit unit can be further miniaturized. Furthermore, because the top electrode of the thin film capacitor is served also as the bonding pad that is wire-bonded to the top side electrode of the semiconductor bare chip, the lead inductance between the thin film capacitor and the semiconductor bare chip is reduced, and the deterioration of high frequency characteristic is prevented.